The products: Age-defying products that target wrinkles or gray hairs are missing one of the real driving forces behind aging. Over the years, cells throughout the body lose mitochondria, tiny powerhouses that provide energy for all sorts of vital functions. This cellular power-outage is one reason older people limp along with a fraction of the zip and pep that they enjoyed in earlier days.

Aging mitochondria may do more than sap energy. In recent years, some scientists have speculated that worn-out power factories in the cells may contribute to a host of age-related problems including memory loss, Parkinson's disease and Type 2 diabetes.

If it were somehow possible to restore mitochondria, they reason, it might also be possible to reclaim some youthful health and vigor. That's the premise behind Juvenon, a widely advertised "anti-aging" supplement that contains alpha lipoic acid (ALA) and acetyl-L-carnitine (ALCAR), two natural compounds that could -- in theory, at least -- give mitochondria a boost. ALA is a strong antioxidant that may help protect mitochondria from age-related damage, and ALCAR is a molecule that helps deliver fuel into the mitochondrial furnaces.

Animal studies from a few years back provided the first evidence that ALA and ALCAR could bring new life to aging mitochondria. As a researcher noted in a 2002 press release from UC Berkeley, old rats fed the compounds "got up and did the Macarena." (No word on how rats discovered this dance fad or what they'd do now. Maybe crunking.)

Juvenon, sold over the Internet and through phone orders, is not available in stores. Each tablet contains 500 milligrams of ALCAR and 200 milligrams of ALA. Users are instructed to take two tablets each day with food. A bottle of 60 tablets -- a month's supply if you follow the directions -- costs about $34.

Other companies have entered Juvenon's territory. A month's supply of an ALCAR and ALA supplement from GNC costs about $20 per month.

"People feel better mentally and physically," says Ben Treadwell, Juvenon's director of research and a former associate professor at Harvard Medical School. Users tend to report a surge of energy within about three weeks, he says, along with better sleep and vivid dreams. But according to Treadwell, the supplement can't stop the aging clock completely and probably won't increase a person's life span.

The bottom line: ALCAR and ALA have been much more thoroughly tested in animals than in humans, and lots of products that seemed promising in the rodent world never really panned out for people. Still, there's some reason to believe that the compounds really can give aging people a boost physically and mentally, says Jiankang Liu, a professor of nutritional science at the University of Kentucky College of Medicine. (Liu is a former consultant for Juvenon but has no current ties to the company.)

"It might not be appropriate to say that you can reverse normal aging, but at least you can slow it down," Liu says. "[Juvenon] should definitely give a person more energy. If you have more mitochondria, you'll have more energy."

Liu says the supplement is most likely to benefit people over 50. "It's not for young, healthy people." He also says that any product containing similar amounts of ALA and ALCAR would likely be as effective.

Liu has authored and co-authored several studies on ALA and ALCAR that found, among other things, that the compounds replenished mitochondria, improved blood sugar control and strengthened the immune systems in diabetic rats. In a review article published this year, Liu concluded that ALA and ALCAR reliably improve the memory and thinking skills of aging mice and rats. These benefits probably cross species lines, he says. In his review, Liu states that ALA and ALCAR should be able to help treat dementia and age-related memory loss in humans.

A four-year study of 43 Alzheimer's patients published in 2007 offers some reason for hope. After taking 600 milligrams of ALA every day, patients held on to their thinking skills much longer than expected. But the study wasn't placebo-controlled, and researchers cautioned that the benefits have yet to be confirmed in bigger, better studies.

Claims that ALA and ALCAR offer youth in a bottle are far-fetched, but the nutrients can help brain cells do their jobs, says Dr. Roger McIntyre, an associate professor of psychiatry and pharmacology at the University of Toronto. In a 2008 report in the journal Expert Opinion on Investigational Drugs, McIntyre and colleagues suggest that the compounds might help people with major depression regain some of the mental sharpness so often lost to the disease. "If someone has tried proven therapies such as cognitive behavioral therapy and antidepressants but still suffers from cognitive trouble, [supplements] might be worth a try."

Because most of the evidence still comes from labs equipped with rat mazes -- and because nobody knows if long-term use might cause side effects in humans -- McIntyre says it's too soon to recommend ALA and ALCAR as go-to treatments.

The final verdict on ALA and ALCAR has yet to come down, agrees Dr. Gjumrakch Aliev, a research associate professor of cardiovascular and neuropathology at the University of Texas at San Antonio. His studies -- including an upcoming paper showing that ALA and ALCAR improved the learning ability of mice with a condition akin to Alzheimer's disease -- have convinced him that the compounds can help stave off age-related memory loss. But, he says, researchers have yet to determine the full effects of the compounds -- positive and negative -- and which doses will work best.

"I don't want to say that everybody should go to the store and get it," he says, "but I'm optimistic."

Liu adds that Juvenon -- or any other ALA and ALCAR supplement -- could never replace the age-fighting benefits of a healthy lifestyle.

"I recommend exercise and balanced nutrition for older people," he says. "There are more important things than taking pills."

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